The present disclosure relates generally to an apparatus and method for providing input/output voltage signals between connected circuit boards, and particularly to an apparatus and method for automatically providing the appropriate input/output voltage signals to the connected circuit board.
PCI (Peripheral Component Interconnect) Mezzanine Cards (PMC) include two classes of input/output (I/O) expansion cards: those that operate with 3.3 volt logic, and those that operate with 5.0 volt logic. The voltage signal used by PMCs is referred to as a VIO (voltage input/output) voltage signal. In order to prevent mismatches between host cards that support one type of logic and expansion cards that support a different type of logic, a mechanical keying pin is employed at the host board. The position of the keying pin on the host board prevents the insertion of an incompatible PMC. Universal PMCs are available that can operate with the host boards using either 3.3 volt logic or 5.0 volt logic. In order to provide a host board that may use either 3.3 volt logic or 5.0 volt logic, so that the host board is compatible with all PMCs (3.3 volt, 5.0 volt, and universal), the VIO signals to the PMC sites are switched to the appropriate voltage level, and the keying pin is positioned accordingly. However, if the voltage switching and keying pin positioning are not matched properly, an incorrect VIO voltage signal may be applied to the PMC expansion card.
Accordingly, there is a need in the art for an apparatus and method for providing properly matched VIO signals between host and expansion boards that overcomes these drawbacks.